1. Field of the Invention
This invention relates to an improved process for bonding cellulosic and/or ligno-cellulosic materials in the production of synthetic board products by utilizing a polyester polyol/polyisocyanate binder.
2. Description of the Prior Art
Many board products are manufactured by the basic process of consolidating or joining together bodies of cellulosic and/or ligno-cellulosic materials using pressure, heat and a chemical binder. Typical binders used in making such products are thermosetting resins such as phenol-formaldehyde, resorcinol-formaldehyde, melamine-formaldehyde, urea-formaldehyde, modified lignosulfonates, urea-furfural and condensed furfuryl alcohol resins. Another binder system involves the use of organic polyisocyanates, either alone or in combination with other binder materials, such as urea-or melamine-formaldehyde resins, phenol-formaldehyde resins, lignosulfonates, furfurals, etc.
The use of polyisocyanate binders in the production of board products is subject to the drawbacks that the isocyanates generally are more expensive than the commonly used formaldehyde binder systems, and the boards produced with the isocyanates have a tendency to adhere to the platens used in their formation. This adhesion can damage or even ruin the board product, and the subsequent cleanup of the contaminated platens is difficult, time-consuming and costly.
Various attempts have been made to overcome this adhesion problem without sacrificing other desirable board properties. Conventional release agents such as oils, wax polishes, silicones and polytetrafluoroethylene have been tried and found wanting.
Another approach involves incorporating into organic polyisocyanate-based binders various additives as internal agents to reduce sticking and produce articles of good quality. For example, U.S. Pat. No. 4,100,328 discloses the use of a polyether polyol-organic polyisocyanate binder composition for bonding cellulosic materials and eliminating sticking to mold faces. Unfortunately, in this binder composition a portion of the rather costly isocyanate component is replaced by polyols which themselves are relatively expensive materials.
The use of polyols in general as reactive additives for polyisocyanate binder compositions is disclosed in U.S. Pat. No. 4,546,039, wherein the polyols are used to prepare isocyanate group-containing prepolymer bonding agents. U.S. Pat. No. 4,609,513 also discloses the usefulness in isocyanate binder systems of polyols generally, including the expensive polyether polyols of the Gallagher patent referred to above. This patent further discloses the need for the concomitant incorporation of a fatty acid component to manufacture board products having acceptable properties.